Circulating leukocyte sequestration in pulmonary capillaries is arguably the initiating event of lung injury in Acute Respiratory Distress Syndrome (ARDS). We present here a microfluidic investigation of the roles of actin organization and myosin II activity during the different stages of leukocyte trafficking through narrow capillaries (entry, transit and shape relaxation) using specific drugs (Latrunculin A, Jasplakinolide and Blebbistatin). The deformation rate during entry reveals that cell stiffness depends strongly on F-actin organization and hardly on myosin II activity, supporting microfilament role in leukocyte sequestration. In the transit stage, cell friction is influenced by stiffness, demonstrating that the actin network is not completely broken after a forced entry into a capillary. Conversely, membrane unfolding was independent of leukocyte stiffness. The surface area of sequestered leukocytes increased by up to 160% in absence of myosin II activity, showing the major role of molecular motors on microvillus wrinkling and zipping. Finally, cell shape relaxation was largely independent of both actin organization and myosin II activity, whereas a deformed state was required for normal trafficking through capillary segments.
Adhesion & Inflammation, INSERM U600, CNRS UMR6212, Université de la méditerranée, Marseille